Anthropic have prices they charge for their models. These prices are what you pay if you use the API, and they are also what you pay if you are an "enterprise" customer - generally any company with 150+ employees.
I haven't seen Anthropic raise the prices of an existing model after it has launched. They sometimes raise prices when they ship a model - Fable is $10/$50 where Opus 4.8 is $5/$25.
They also have monthly subscriptions for individuals, which are a notoriously good deal. THOSE are definitely less trustworthy and predictable than the API list prices, since the subscription allowed quotas can and have changed in the past.
What am I missing here?
You can chose to trust me or not based on my track record.
From your posting history it looks like you have a whole lot more relevant experience with enterprise software deals than I do. Have you learned anything interesting about how Anthropic pricing works?